Protein sulfonic acid modification is a less common but important modality of protein post-translational modification. It involves adding a sulfonic acid group to a specific amino acid residue of a protein, usually a tyrosine residue. Unlike phosphorylation, sulfonylation is a covalent, permanent modification.
Figure 1Schematic diagram of the identification of protein post-translational modifications.
The commonly used methods for detecting protein sulfonation are mainly as follows:
1. Mass spectrometry (MS):
Due to the increased mass due to sulfonation, LC-MS MS can be used to identify sulfonation sites. However, sulfonylated peptides may lose sulfonic acid groups in MS, which makes identification challenging. Data interpretation for MS often requires specific bioinformatics tools to ensure proper identification of sulfonylation sites.
2. Western blot and sulfonylated specific antibodies:
Sulfonation status can be detected by Western blot using antibodies specific to sulfonylated proteins or sulfonylation sites.
3. Immunofluorescence staining
Using sulfonylation-specific antibodies, sulfonylated proteins can be localized on cell or tissue sections by immunofluorescence staining.
4. Enzyme-linked immunosorbent assay (ELISA):
Using sulfonation-specific antibodies, ELISAs can be designed for quantification of sulfonated proteins.